Where a substance of volume of material is of relatively uniform moisture content, it is relatively easy to obtain a representative sample thereof and to measure the moisture content of that sample in order to obtain knowledge of the moisture content of the volume of the substance.
However, where it is required to determine the moisture content of a continuous flow of substance during production or a processing operation of that substance, further difficulties arise due to the variation of the moisture content of the substance along its travel, and more particularly to the variation of the moisture content in the depth of the substance together with variations of the depth of the substance itself.
In U.S. Pat. No. 4,468,610 there is described an apparatus for measuring the moisture content of gypsum board and like products, and in this instance the gypsum board is of regular thickness and density, and the moisture content does not readily vary through the thickness of the board itself.
In Australian Patent Specification No. 52496/86 there is described a method and apparatus for producing a signal or signals related to the moisture content of a substance as it travels along a conveyor belt, this apparatus utilizing a single pair of spaced electrodes located remote from the substance whereby an A.C. field generated therebetween passes through the substance and means measuring an A.C. signal related to a field passing through the substance to derive a moisture output signal therefrom related to the moisture content of the substance. Also that Patent specification describes an apparatus for producing signals related to the density or thickness of the substance and these two apparatuses are combined within the one unit in order to provide a signal representative of the moisture content of the substance.